Exception in Application start method

Question

I'm trying to create a JavaFX program, and whenever I try to run it I get the message "Exception in Application start method" in console with a wall of codes
can anyone help me fix that?

Answer 1

it was running smoothly, but suddenly it stopped running , I don't know why

Answer 2

It's not a copy-paste or spam question, and it's the the same, everytime a different problem in JavaFX, is it forbidden to ask? Martin Taylor